I typically run DNG Converter over a folder tree to convert all camera RAW files within to DNG files, saving the DNGs in the same folder with the same filename (other than extension). So, for example, if I have:

C:\Photos\Image1.crw

C:\Photos\Image2.crw

After conversion, I'll have:

C:\Photos\Image1.crw

C:\Photos\Image1.dng

C:\Photos\Image2.crw

C:\Photos\Image2.dng

Currently, if I run DNG Converter on a folder that has some images that have already been converted, DNG Converter creates new copies from the existing raw and DNG files. So if I have a folder with the following files:

C:\Photos\Image1.crw

C:\Photos\Image1.dng

C:\Photos\Image2.crw

C:\Photos\Image2.dng

C:\Photos\Image3.crw

C:\Photos\Image4.crw

After conversion, I'll have:

C:\Photos\Image1.crw

C:\Photos\Image1.dng

C:\Photos\Image1_1.dng (created from Image1.crw)

C:\Photos\Image1_2.dng (created from Image1.dng)

C:\Photos\Image2.crw

C:\Photos\Image2.dng

C:\Photos\Image2_1.dng (created from Image2.crw)

C:\Photos\Image2_2.dng (created from Image2.dng)

C:\Photos\Image3.crw

C:\Photos\Image3.dng

C:\Photos\Image4.crw

C:\Photos\Image4.dng

What I really want is for Image3 and Image4 to be converted, while ignoring Image1 and Image2, which have already been converted.

Optionally, if Image1.dng and Image2.dng are an older DNG version or have been converted using different conversion settings than I'm using now, I may want those images reconverted or updated, overwriting the existing DNG. (Depending on the specific circumstances, this might be a little tricky, since if I've made any adjustments to the existing DNG in Lightroom or Camera Raw, I would want those updates preserved in the new DNG.)